If you’re sick of throwing your worn burrs away, try this: First,
clean your worn burrs thoroughly.I use a 20% sodium hydroxide
solution warmed on a hot plate followed by steam cleaning. Dip the
cleaned burrs in concentrated nitric acid and let the acid work for a
half minute or less, then steam clean again. Your burrs should be
sharpened. Nitric acid doesn’t work on high speed steel and some
other metals. The burrs will be slightly smaller each time you repeat
the process. The results are just short of miraculous. I’m a
completely self-tought jeweller so my apologies if this is a well
known process.
Robert Hood